Pcv valve mounting structures

ABSTRACT

A mounting structure for mounting a PCV valve includes a mount recess formed in at least one of joint surfaces of a cylinder head and an intake manifold, so that at least a part of the PCV valve can be fitted into the mount recess.

This application claims priority to Japanese patent application serialnumber 2010-034625, the contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to mounting structures for PCV valves(positive crankcase ventilation valves) used for controlling flow ofblow-by gas.

2. Description of the Related Art

A known PCV valve mounting structure is disclosed, for example, inJapanese Laid-Open Publication No. 6-229221. The mounting structuredisclosed in this publication is shown in a vertical sectional view inFIG. 6.

As shown in FIG. 6, according to the known mounting structure, a baseend portion (lower end portion as viewed in FIG. 6) of a PCV valve 130is mounted to a cylinder head cover 110, and a base end portion (upperend portion as viewed in FIG. 6) of the PCV valve 130 is mounted to asurge tank 112. More specifically, a flat valve mounting portion 120 isformed on the upper portion of the cylinder head cover 110, and a valvemounting hole 136 is formed in the valve mounting portion 120. The baseend portion of the PCV valve 130 is inserted into the valve mountinghole 136, so that a gas inlet port 142 formed at the base end portion ofthe PCV valve 130 communicates with inside of the cylinder head cover110. A flat valve mounting portion 122 is formed on the lower portion ofthe surge tank 112, and a valve mounting hole 144 is formed in the valvemounting portion 122. A terminal end portion of the PCV valve 130 isinserted into the valve mounting hole 144. Therefore, a gas reflux port150 formed at the terminal end portion of the PCV valve 130 communicateswith inside of the surge tank 112. When a load is applied to an engine,a negative pressure is produced by an intake air and can operate the PCVvalve 130 mounted to the cylinder head cover 110 and the surge tank 112as described above for adjusting the amount of the brow-by gas refluxedfrom within the cylinder head 110 to the surge tank 112 when the brow-bygas produced at the engine is refluxed into an intake air system of theengine.

In the case of the known mounting structure, the base end portion of thePCV valve 130 is inserted into the valve mounting hole 136 while theterminal end portion of the PCV valve 130 is inserted into the valvemounting hole 144 formed in the valve mounting portion 122 of the surgetank 112. However, an intermediate portion of the PCV valve 130positioned between the base end portion and the terminal end portion isexposed to the outside at a position between the cylinder head cover 110and the surge tank 112. Therefore, if the intermediate portion of thePCV valve 130 is exposed to the atmospheric air (in particular, airstream produced during running of a vehicle) when the atmospheric air isat an extremely low temperature, a water content contained in theblow-by gas flowing through the PCV valve 130 from the gas inlet port142 to the gas reflux port 150 may be frozen.

Therefore, there is a need in the art for a PCV valve mounting structurethat can inhibit or prevent, a water content contained in the blow-bygas from being frozen up within the PCV valve.

SUMMARY OF THE INVENTION

A mounting structure for mounting a PCV valve includes a mount recessformed in at least one of joint surfaces of a cylinder head and anintake manifold, so that at least a part of the PCV valve can be fittedinto the mount recess when the cylinder head and the intake manifold arejoined together at the joint surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a blow-by gas refluxing deviceincorporating a PCV valve mounting structure according to a firstexample;

FIG. 2 is a sectional view showing the PCV valve mounting structure;

FIG. 3 is a sectional view similar to FIG. 2 but showing a PCV valvemounting structure according to a second example;

FIG. 4 is a sectional view similar to FIG. 2 but showing a PCV valvemounting structure according to a third example;

FIG. 5 is a sectional view similar to FIG. 2 but showing a PCV valvemounting structure according to a fourth example; and

FIG. 6 is a sectional view showing a PCV valve mounting structureaccording to a known art.

DETAILED DESCRIPTION OF THE INVENTION

Each of the additional features and teachings disclosed above and belowmay be utilized separately or in conjunction with other features andteachings to provide improved PCV valve mounting structures.Representative examples of the present invention, which examples utilizemany of these additional features and teachings both separately and inconjunction with one another, will now be described in detail withreference to the attached drawings. This detailed description is merelyintended to teach a person of skill in the art further details forpracticing preferred aspects of the present teachings and is notintended to limit the scope of the invention. Only the claims define thescope of the claimed invention. Therefore, combinations of features andsteps disclosed in the following detailed description may not benecessary to practice the invention in the broadest sense, and areinstead taught merely to particularly describe representative examplesof the invention. Moreover, various features of the representativeexamples and the dependent claims may be combined in ways that are notspecifically enumerated in order to provide additional useful examplesof the present teachings.

In one example, a mounting structure for mounting a PCV valve includes amount recess formed in at least one of joint surfaces of a cylinder headand an intake manifold for joining to the joint surface of the cylinderhead. At least a part of the PCV valve can be fitted into the mountrecess. When the cylinder head and the intake manifold are joinedtogether at the joint surfaces, the PCV valve is accommodated within atleast one of the cylinder head and the intake manifold at a positionproximal to or across the joint surfaces.

Therefore, it is possible to protect the entire PCV valve from theinfluence of the atmospheric air (in particular, air stream producedduring running of a vehicle). As a result, it is possible to prevent awater content contained in the blow-by gas from being frozen within thePCV valve.

Further, by joining the cylinder head and the intake manifold togetherafter fitting the PCV valve into the mount recess formed in one of thejoint surfaces, the PCV valve can easily be brought to be accommodatedwithin at least one of the cylinder head and the intake manifold.

In the case that only a part of the PCV valve can be fitted into themount recess, the mounting structure may further include a fittingrecess formed in the other of the joint surfaces and capable of fittingwith the other part of the PCV valve.

In this case, it is possible to position the cylinder head and theintake manifold relative to each other due to fitting of the fittingrecess with the other part of the PCV valve when the cylinder head andthe intake manifold are joined together.

A resilient member may be provided for pressing the PCV valve againstthe cylinder head, so that the PCV can be held in contact with thecylinder head. With this arrangement, the heat of the engine can beefficiently transmitted to the PCV valve to further reliably prevent thewater content from being frozen within the gas passage of the PCV valve.

The PCV valve may have a valve case made of resin. The resin valve casecan be manufactured at a lower cost and may be lighter in weight incomparison with the case that the valve case is made of metal.

The mounting structure may further include a sealing device for sealingbetween the joint surfaces at a position around the PCV valve.

Various examples will now be described with reference to the drawings.

First Example

A PCV valve mounting structure according to a first example is used tobe provided in a blow-by passage of a blow-by gas refluxing device thatcan reflux blow-by gas into an intake air system of an engine. Morespecifically, the blow-by gas may leak from between a piston ring and acylinder wall of the engine into a crank chamber. For the purpose ofexplanation, a general construction of the blow-by gas refluxing devicewill be first described, and the PCV valve mounting structure will beexplained after that.

Referring to FIG. 1, a cylinder head cover 14 is mounted to a cylinderhead 12 of an engine 10. A baffle plate 16 is mounted between thecylinder head 12 and the cylinder head cover 14, so that an internalspace defined between the cylinder head 12 and the cylinder head cover14 is divided into a cam chamber 17 and an oil separator chamber 18disposed on a lower side and an upper side of the internal space,respectively. The cam chamber 17 communicates with a crank chamber (notshown) of the engine 10. An opening (not shown) is formed in the baffleplate 16 for communicating between the cam chamber 17 and the oilseparator chamber 18. The oil separator chamber 18 is configured to beable to separate an oil content, such as oil droplets and oil mist, fromthe blow-by gas and to return the oil content into the cam chamber 17.Although not shown in FIG. 1, a cam mechanism for driving intake valvesand exhaust valves is disposed within the cam chamber 17. Intake portsand exhaust ports (not shown) are formed in the cylinder head 12 andcommunicate with respective combustion chambers. The intake valves andthe exhaust valves are disposed at the cylinder head 12. The cylinderhead 12 is secured to a cylinder block (not shown).

A flange 21 formed on the downstream end of an intake manifold 20 isjoined to the cylinder head 12 by a suitable fastening device. Theintake manifold 20 is made of resin and has a surge tank 23 forintroducing intake air (fresh air) thereinto and distribution pipes 24communicating with a downstream side of the surge tank 23 fordistributing the intake air from the surge tank 23 into respectiveengine cylinders. The distribution pipes 24 communicate with the intakeports (not shown) formed in the cylinder head cover 14. Although notshown in FIG. 1, a throttle valve for controlling the flow rate of theintake air is disposed on the upstream side of the surge tank 23 of theintake manifold 20, and an air cleaner is disposed on the upstream sideof the throttle valve. The air cleaner, the throttle device and theintake manifold 20, etc., constitute an intake air system forintroducing intake air into the intake ports of the cylinder head 12. Inplace of the fastening device, clips, a snap-fitting device or any othersuitable device can be used for joining the intake manifold 20 to thecylinder head 12.

The oil separator chamber 18 and an intake air passage (not shown)defined within the intake manifold 20 communicate with each other via ablow-by gas passage 26. The blow-by gas passage 26 includes a firstpassage portion 27, a second passage portion 28 and a third passageportion 29. The second passage portion 27 is formed in the cylinder head12 and has an L-shaped configuration. An upstream end (upper end) of thesecond passage portion 28 is open into the cam chamber 17. A downstreamend (lower end) of the second passage portion 28 extends laterally(rightward in FIG. 1) and is open at a joint surface 12 a where thecylinder head 12 is joined to the flange portion 21 of the intakemanifold 20. The first passage portion 27 is defined in a gasintroduction pipe 31 that is inserted into an upstream end (upper end)of the second passage portion 28 so as to be joined thereto. The oilseparator chamber 18 and the second passage portion 28 communicate witheach other via the first passage portion 27.

The third passage portion 29 is formed in the intake manifold 20.Referring to FIG. 2, an upstream end (left end as viewed in FIG. 2) ofthe third passage portion 29 is opened at a joint surface 20 a of theintake manifold 20 for joining to the joint surface 12 a of the cylinderhead 12. A downstream end (not shown) of the third passage portion 29communicates with the intake air passage defined in the intake manifold20 (i.e., the passages defined in the distributing pipes 24 or theinternal space within the surge tank 23). The upstream end of the thirdpassage portion 29 and the downstream end of the second passage portion28 communicate with each other in a manner like a straight path and havethe same axis. In the path of the blow-by gas passage 26, morespecifically, at a position between the joint surface 12 a of thecylinder head 12 and the joint surface 20 a of the intake manifold 20, aPCV valve (positive crankcase ventilation valve) 34 is provided. Theconstruction of the PCV valve 34 will be explained later.

During the operation (driving) of the engine, the negative pressure ofthe intake air (hereinafter called “intake air negative pressure” withinthe intake manifold 20 is applied to a crank chamber (not shown) of theengine via the blow-by gas passage 26, the oil separator chamber 18 andthe cam chamber 17. Therefore, blow-by gas produced in the crank chamberis refluxed into the intake manifold 20 via the cam chamber 17, the oilseparator chamber 18 and the first to third passage portions 27, 28 and29 of the blow-by gas passage 26. Accordingly, fresh air (external air)is introduced into the crank chamber via a fresh air introductionpassage (not shown). During refluxing of the blow-by gas, the PCV valve34 operates in response to the load condition of the engine or theintake air negative pressure to control the amount of flow or the flowrate of the refluxing blow-by gas that flows from the second passageportion 28 to the third passage portion 29 of the blow-by gas passage26. The blow-by gas passage 26 and the PCV valve 34 constitute a blow-bygas refluxing device 36.

The mounting structure for mounting the PCV valve 34 will now bedescribed with reference to FIG. 2. First, the construction of the PCVvalve 34 will be described. The PCV valve 34 has a valve case 38 that ismade of resin and has a hollow cylindrical configuration. The valve case38 is separated into a main case member 39 and an auxiliary case member40 along an axial direction. A connecting side end portion (right endportion as viewed in FIG. 2) of the main case member 39 is coaxiallyfitted on a connecting side end portion (left end portion as viewed inFIG. 2) of the auxiliary case member 40, so that a gas passage 42 isdefined by the internal spaces of the main and auxiliary case members 39and 40 so as to extend therebetween. The valve case 38 has an outershape like a stepped shaft with a leading end portion (right endportion) of the auxiliary case member 40 forming a small diameterportion of the stepped shaft. For the purpose of explanation, an endportion (left end portion as viewed in FIG. 2) of the main case member39 on the side opposite to the connecting side end portion will bereferred to as a base end portion of the PCV valve 34 or a base endportion of the valve case 38, and an end portion (right end portion asviewed in FIG. 2) will be referred to as a leading end portion of thePCV valve 34 or a leading end portion of the valve case 38.

An opening formed at the base end portion of the valve case 38 serves asa gas inlet port 42 a of the gas passage 42. On the other hand, anopening formed at the leading end portion (or a small diameter portion)of the valve vase 38 serves as a gas outlet port 42 b of the gas passage42. A valve seat 44, a valve member 46 and a valve spring 48 aredisposed within the internal space defined in the main case member 39.The valve seat 44 has a configuration like an annular plate. The outerperipheral portion of the valve seat 44 is held between the main andauxiliary case members 39 and 40. The internal space of the main casemember 39 serves as a valve chamber that receives the valve member 46and the valve spring 48 therein and communicates with the internal spaceof the auxiliary case member 40 through a central hole formed in thevalve seat 44.

The valve member 46 has a substantially cylindrical configuration and isreceived within the internal space of the main case member 39 so as tobe movable in an axial direction (right and left direction in FIG. 2).The leading end portion (right end portion as viewed in FIG. 2) of thevalve member 46 is tapered toward the leading end and has a diameterdecreasing toward the leading end so as to be insertable into thecentral hole of the valve seat 44. The valve spring 48 is disposedbetween the valve seat 44 and the valve member 46. The valve spring 48is a coil spring and normally biases the valve member 46 toward the gasinlet port 42 a (leftward as viewed in FIG. 2). Therefore, when thevalve member 46 moves forwardly in the axial direction (rightwardly asviewed in FIG. 2), a clearance or a cross sectional area of a passagedefined between the valve seat 44 and the valve member 46 changes, sothat a flow rate of the blow-by gas flowing through the PCV valve 34 canbe controlled.

A buffer spring 50 is a coil spring and is disposed within the auxiliarycase member 40. When the valve member 46 has moved to its maximum strokeend, the leading end of the valve member 46 may contact the bufferspring 50. With this arrangement, it is possible to prevent the leadingend portion of the valve member 46 from being offset from the axis ofmovement of the valve member 46 and from being swung as the valve member46 moves to its maximum stroke end. In this example, the components,such as the valve seat 44, the valve member 46, the valve spring 48 andthe buffer spring 50, of the PCV valve 34 other than the valve case 38are made of metal. However, at least one of these components (such asthe valve seat 44, the valve member 46, the valve spring 48 and thebuffer spring 50) other than the valve case 38 may be made of resin.

The structure for mounting the PCV valve 34 will now be described. Amount recess 52 is formed in the joint surface 20 a of the intakemanifold 20 so as to communicate with the upstream end of the thirdpassage portion 29. In this example, the mount recess 52 is configuredlike a bore coaxial with the upstream end of the third passage portion29 and having a diameter larger than that of the upstream end of thethird passage portion 29. In the following explanation, the upstream endof the third passage portion 29 positioned proximal to the mount recess52 will be referred to as a small diameter passage part of the thirdpassage portion 29. A large diameter portion of the valve case 38 of thePCV valve 34 is fitted into the mount recess 52, while the leading endportion (or a small diameter portion) of the PCV valve 34 is fitted intothe small diameter passage part of the third passage portion 29.Therefore, the gas outlet port 24 b of the valve case 38 of the PCVvalve 34 communicates with the small diameter passage part of the thirdpassage portion 29. An O-ring 54 is fitted on the base end portion ofthe valve case 38 so as to resiliently contact the inner circumferentialsurface of the mount recess 52. An O-ring 55 is fitted on the leadingend portion (small diameter portion) of the valve case 38 so as toresiliently contact the inner circumferential surface of the smalldiameter passage part. In this example, a stepped surface formed betweenthe large diameter portion and the small diameter portion of the valvecase 38 is positioned to be proximate to or contact with a steppedsurface 58 formed between the mount recess 52 and the small diameterpassage part of the third passage portion 29 of the intake manifold 20.

The intake manifold 20 having the PCV valve 34 mounted thereto asdescribed above is then joined to the cylinder head 12, so that the PCVvalve 34 is accommodated within the intake manifold 20 at a positionproximal to the joint surfaces 12 a and the 20 a. In addition, the gasinlet port 42 a of the valve case 38 of the PCV valve 34 is brought tocommunicate with the second passage portion 28 of the cylinder head 12.Further, a part of the joint surface 12 a of the cylinder head 12defining the peripheral edge of the downstream end of the second passageportion 28 is proximate to or contact with a base end surface 61 or anend surface of the base end portion of the valve case 38. A gasket 56 isfitted into a corresponding recess formed in the joint surface 20 a in amanner surrounding the mount recess 52 and resiliently contacts thejoint surface 12 a of the cylinder head 12.

According to the PCV valve mounting structure of the above example, thePCV valve 34 is accommodated within the intake manifold 20 at a positionproximal to the joint surface 12 a of the cylinder head 12 and the jointsurface 20 a of the intake manifold 20 by fitting the PCV valve 34 intothe mount recess 52 formed in the joint surface 20 a of the intakemanifold 20. Therefore, it is possible to protect the entire PCV valve34 from the influence of the atmospheric air (in particular, air streamproduced during miming of a vehicle) by the cylinder head 12 and theintake manifold 20. As a result, it is possible to prevent the watercontent of the blow-by gas from being frozen within the gas passage 42of the PCV valve 34.

Further according to the above mounting structure, it is possible toeasily accommodate the PCV valve 34 within the intake manifold 20 at aposition proximal to the joint surface 12 a of the cylinder head 12 andthe joint surface 20 a of the intake manifold 20 by joining the cylinderhead 12 and the intake manifold 20 together with the PCV valve 34 fittedinto the mount recess 52 formed in the joint surface 20 a of the intakemanifold 20.

Furthermore, the assembling operation of the PCV valve 34 can beefficiently made by joining the cylinder head 12 and the intake manifold20 together with the PCV valve 34 fitted into the intake manifold 20.

Furthermore, the valve case 38 (including the main and auxiliary casemembers 39 and 40) of the PCV valve 34 is made of resin. Therefore, itis possible to reduce the manufacturing cost and the weight of the PCVvalve 34 in comparison with the case that the valve case 38 is made ofmetal.

Second Example

A second example will now be described with reference to FIG. 3 that isa sectional view showing a PCV valve mounting structure according tothis example. The second example is a modification of the first example,and therefore, like members are given the same reference numerals as thefirst example and the description of these members will not be repeated.

Referring to FIG. 3, according to the second example, the steppedsurface 58 of the mount recess 52 of the intake manifold 20 and thestepped surface 60 of the valve case 38 of the PCV valve 34 are spacedfrom each other by a predetermined distance. In order to provide such aspace between the stepped surfaces 58 and 60, the length in the axialdirection (depth) of the mount recess 52 of the intake manifold 52 isset to be longer than that of the mount recess 52 of the first example.

A pressing spring 62 serving as a resilient member is interposed betweenthe stepped surfaces 58 and 60. The pressing spring 62 may be made, forexample, of metal, and is loosely fitted on the leading end portion(small diameter portion) of the valve case 38. Therefore, by the biasingforce of the pressing spring 62, the valve case 38 or the PCV valve 34is pressed toward the cylinder head 12, so that the base end surface 61of the valve case 38 is held in contact with the joint surface 12 a ofthe cylinder head 12. Further, the stepped surfaces 58 and 60 haveannular grooves 58 a and 60 a, respectively, into which opposite endportions of the pressing spring 62 can be fitted.

According to the PCV valve mounting structure of this example, thepressing spring 62 is provided for pressing the PCV valve 34 against thecylinder head 12. Therefore, the PCV valve 34 can be held in contactwith the cylinder head 12. As a result, it is possible to efficientlytransmit the heat of the engine 10 (see FIG. 1) to the valve case 38 ofthe PCV valve 34 for further effectively prevent the water content ofthe blow-by gas from being frozen within the gas passage 42 of the PCVvalve 34. In addition, it is possible to absorb potential displacementin the axial direction of the valve case 38 of the PCV valve 34 by theresiliency of the pressing spring 62. Further, because the opposite endportions of the pressing spring 62 are fitted into the annular grooves58 a and 60 a of the stepped surfaces 58 and 60, it is possible tostably support the pressing spring 62. The pressing spring 62 may bereplaced with any other resilient member, such as a leaf spring and acushion rubber.

Third Example

A third example will now be described with reference to FIG. 4 that is asectional view showing a PCV valve mounting structure according to thisexample. The third example is a modification of the second example, andtherefore, like members are given the same reference numerals as thesecond example and the description of these members will not berepeated.

Referring to FIG. 4, according to the third example, a fitting recess 64is formed in the joint surface 12 a of the cylinder head 12 andcommunicates with the downstream end of the second passage portion 28.More specifically, the fitting recess 64 is coaxial with the downstreamend of the second passage portion 28 and has a diameter larger than thatof the downstream end of the second passage portion 28. In the followingexplanation, the downstream end of the second passage portion 28positioned proximal to the fitting recess 64 will be referred to as asmall diameter passage part of the second passage portion 28.

In the third example, the axial length of the main case member 39 of thevalve case 38 is set to be longer than that of the second example shownin FIG. 3, so that the base end portion of the valve case 38 extendsfrom the joint surface 20 a of the intake manifold 20 by a predetermineddistance. The base end portion of the valve case 38 extending from thejoint surface 20 a is fitted into the fitting recess 64, so that the gasinlet port 42 a of the valve case 38 of the PCV valve 34 communicateswith the small diameter passage part of the second passage portion 28.The base end surface 61 of the valve case 38 is held in contact with astepped surface 65 formed within the cylinder head 12 at a positionbetween the fitting recess 64 and the small diameter passage part of thesecond passage portion 28.

According to the mounting structure of the PCV valve 34 of this example,the base end portion of the valve case 38 of the PCV valve 34 is fittedinto the fitting recess 64 formed in the joint surface 12 a of thecylinder head 12. Therefore, the cylinder head 12 and the intakemanifold 20 can be positioned relative to each other when they arejoined together. In addition, because the base end portion of the valvecase 38 of the PCV valve 34 is fitted into the fitting recess 64 formedin the joint surface 12 a of the cylinder head 12, the heat of theengine 10 (see FIG. 1) can be efficiently transmitted to the valve case38 of the PCV valve 34, so that the water content contained in theblow-by gas within the gas passage 42 of the PCV valve 34 can be furtherreliably prevented from being frozen.

Fourth Example

A fourth example will now be described with reference to FIG. 5. Thefourth example is a modification of the first example, and therefore,like members are given the same reference numerals as the first exampleand the description of these members will not be repeated.

Referring to FIG. 5, in this example, the large diameter portion of thevalve case 38 of the PCV valve 34 is fitted into a mounting recess 66formed in the joint surface 12 a of the cylinder head 12 in place of themounting recess 52 formed in the joint surface 20 a of the intakemanifold 20 of the first example (see FIG. 2). The mounting recess 66communicates with the downstream end of the second passage portion 28and is configured like a bore coaxial with the downstream end of thesecond passage portion 28 and having a diameter larger than that of thedownstream end of the second passage portion 28. In the followingexplanation, the downstream end of the second passage portion 28positioned proximal to the mount recess 66 will be referred to as asmall diameter passage part of the second passage portion 28. The largediameter portion of the valve case 39 of the PCV valve 34 is fitted intothe mount recess 66, so that the gas inlet port 42 a of the valve case38 communicates with the small diameter passage part of the secondpassage portion 28. The leading end portion (small diameter portion) ofthe valve case 38 extends from the joint surface 12 a of the cylinderhead 12. The O-ring 54 fitted on the base end portion of the valve case38 resiliently contacts the inner circumferential surface of the mountrecess 66.

In addition, in this example, the upstream end part of the third passageportion 29 of the intake manifold 20 does not include the mount recess52 as provided in the first example (see FIG. 2) but includes only thesmall diameter passage part. A part of the upstream end part of thethird passage portion 29 including the upstream opening is configured asa fitting recess 68 formed in the joint surface 20 a of the intakemanifold 20.

The cylinder head 12 having the PCV valve 34 mounted therein asdescribed above is joined to the intake manifold 20, so that the PCVvalve 34 is accommodated within the cylinder head 12 at a positionproximal to the joint surface 12 a of the cylinder head 12 and the jointsurface 20 a of the intake manifold 20. In addition, the small diameterportion (leading end portion) of the valve case 38 is fitted into thefitting recess 68 of the third passage 29 of the intake manifold 20, sothat the gas outlet port 42 b of the valve case 38 of the PCV valve 34communicates with the third passage 29. Further, the O-ring 55 fitted onthe valve case 38 resiliently contacts the inner circumferential surfaceof the fitting recess 68 of the third passage portion 29. Furthermore,in this example, the stepped surface 60 of the valve case 38 is proximalto or in contact with the joint surface 20 a of the intake manifold 20.The base end surface 61 of the valve case 30 is proximal to or incontact with a stepped surface 70 formed in the cylinder head 12 at aposition between the mount recess 66 and the small diameter passage partof the second passage portion 28.

According to the PCV valve mounting structure of the fourth example, itis possible to accommodate the PCV valve 34 within the cylinder head 12at a position proximal to the joint surface 12 a of the cylinder head 12and the joint surface 20 a of the intake manifold 20 by joining thecylinder head 12 and the intake manifold 20 together in the state thatthe PCV valve 34 is fitted into the mount recess 66 formed in the jointsurface 12 a of the cylinder head 12.

In addition, the assembling operation of the PCV valve 34 can beefficiently made by joining the cylinder head 12 and the intake manifold20 together with the PCV valve 34 fitted into the cylinder head 12.

Furthermore, the leading end portion (small diameter portion) of thevalve case 38 of the PCV valve 34 is fitted into the fitting recess 68formed in the joint surface 20 a of the intake manifold 20. Therefore,due to fitting of the leading end portion (small diameter portion) ofthe valve case 38 of the PCV valve 34 into the fitting recess 68 formedin the joint surface 20 a of the intake manifold 20, the cylinder head12 and the intake manifold 20 can be positioned relative to each otherwhen they are joined together. It may be possible that the mount recess66 of the cylinder head 12 can be fitted not only with the largediameter portion of the valve case 38 of the PCV valve 34 but with theentire valve case 38 including the small diameter portion.

(Possible Modifications)

Although the blow-by gas passage 26 in the above examples communicateswith the oil separator chamber 18, it may communicate with any otherchamber or passage that communicates with the crank chamber of theengine. Further, although the valve case 38 of the PCV valve 34 is madeof resin, it may be made of metal.

1. A mounting structure for mounting a PCV valve, comprising: a mountrecess formed in one of a joint surface of a cylinder head and a jointsurface of an intake manifold for joining to the joint surface of thecylinder head, wherein: at least a part of the PCV valve can be fittedinto the mount recess; and when the cylinder head and the intakemanifold are joined together at the joint surfaces, the PCV valve isaccommodated within at least one of the cylinder head and the intakemanifold at a position proximal to or across the joint surfaces.
 2. Themounting structure as in claim 1, wherein only a part of the PCV valvecan be fitted into the mount recess.
 3. The mounting structure as inclaim 2, further comprising a fitting recess formed in the other of thejoint surfaces and capable of fitting with the other part of the PCVvalve.
 4. The mounting structure as in claim 1, further comprising aresilient member pressing the PCV valve against the cylinder head. 5.The mounting structure as in claim 1, wherein the PCV valve includes avalve case made of resin.
 6. The mounting structure as in claim 1,further comprising a sealing device for sealing between the jointsurfaces at a position around the PCV valve when the cylinder head andthe intake manifold are joined together at the joint surfaces.
 7. Amounting structure for mounting a PCV valve, comprising: a mount recessformed in one of a joint surface of a cylinder head and a joint surfaceof an intake manifold for joining to the joint surface of the cylinderhead, wherein: the PCV valve can be fitted into the mount recess; thePCV valve has a first end portion and a second end portion positioned onopposite sides in an axial direction; and when the cylinder head and theintake manifold are joined together at the joint surfaces, the PCV valveis accommodated within one of the cylinder head and the intake manifoldin a state that the first end portion is opposed to the other of thejoint surfaces and the second end portion is opposed to a steppedsurface formed in the one of the cylinder head and the intake manifoldand defining a bottom of the mount recess.
 8. The mounting structure asin claim 7, further comprising a biasing device disposed within themount recess at a position between the first end portion of the PCVvalve and the stepped surface, so that the first end portion of the PCVvalve is pressed against the other of the joint surfaces when thecylinder head and the intake manifold are joined together at the jointsurfaces.
 9. A mounting structure for mounting a PCV valve, comprising:a mount recess formed in one of a joint surface of a cylinder head and ajoint surface of an intake manifold for joining to the joint surface ofthe cylinder head, and a fitting recess formed in the other of the jointsurfaces, wherein: the PCV valve has a first end portion and a secondend portion positioned on opposite sides in an axial direction; and whenthe cylinder head and the intake manifold are joined together at thejoint surfaces, the first end portion and the second end portion of thePCV valve are fitted into the mount recess and the fitting recess,respectively.
 10. The mounting structure as in claim 9, wherein when thecylinder head and the intake manifold are joined together at the jointsurfaces, the first end portion of the PCV valve is opposed to a firststepped surface formed in one of the cylinder head and the intakemanifold and defining a bottom of the mount recess, and the second endportion of the PCV valve is opposed to a second stepped surface formedin the other of the cylinder head and the intake manifold and defining abottom of the fitting recess.
 11. The mounting structure as in claim 9,wherein the PCV valve has a stepped portion between the first endportion and the second end portion, and when the cylinder head and theintake manifold are joined together at the joint surfaces, the first endportion is opposed to a stepped surface formed in one of the cylinderhead and the intake manifold and defining a bottom of the mount recess,and the stepped portion is opposed to the other of the joint surfaces.